Evolution of Internal Stresses in Composites during Creep

1994 ◽  
Vol 365 ◽  
Author(s):  
Edgar Lara-Curzio ◽  
M. K. Ferber
Keyword(s):  
Axial Stress ◽  
Elastic Fiber ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Interfacial Stress ◽  
Internal Stresses ◽  
Matrix Composites ◽  
Complete Relaxation ◽  
The Matrix ◽  
Linear Viscoelastic

ABSTRACTThe redistribution of internal stresses in a composite with linear viscoelastic constituents was calculated when the composite is subjected to a constant stress at a temperature where the phases would exhibit time-dependent deformation. It was found for the case of an elastic fiber embedded in a matrix that behaves as a Burgers material under distortion and elastically under dilation, that the normal interfacial stress and the axial stress in the matrix undergo complete relaxation at long times. The implications of these findings are discussed in relation to the behavior of ceramic matrix composites.

Micromechanics Approach for the Overall Elastic Properties of Ceramic Matrix Composites Incorporating Defect Structures

2020 ◽  
Author(s):  
Rajesh S. Kumar
Keyword(s):  
Elastic Properties ◽  
Volume Fraction ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Volume Shrinkage ◽  
Matrix Composites ◽  
Defect Structures ◽  
Linear Elastic ◽  
Elastic Tensor ◽  
The Matrix

Abstract Initial mechanical behavior of Ceramic Matrix Composites (CMCs) is linear until the proportional limit. This initial behavior is characterized by linear elastic properties, which are anisotropic due to the orientation and arrangement of fibers in the matrix. The linear elastic properties are needed during various phases of analysis and design of CMC components. CMCs are typically made with ceramic unidirectional or woven fiber preforms embedded in a ceramic matrix formed via various processing routes. The matrix processing of interest in this work is that formed via Polymer Impregnation and Pyrolysis (PIP). As this process involves pyrolysis process to convert a pre-ceramic polymer into ceramic, considerable volume shrinkage occurs in the material. This volume shrinkage leads to significant defects in the final material in the forms of porosity of various size, shape, and volume fraction. These defect structures can have a significant impact on the elastic and damage response of the material. In this paper, we develop a new micromechanics modeling framework to study the effects of processing-induced defects on linear elastic response of a PIP-derived CMC. A combination of analytical and computational micromechanics approaches is used to derive the overall elastic tensor of the CMC as a function of the underlying constituents and/or defect structures. It is shown that the volume fraction and aspect ratio of porosity at various length-scales plays an important role in accurate prediction of the elastic tensor. Specifically, it is shown that the through-thickness elastic tensor components cannot be predicted accurately using the micromechanics models unless the effects of defects are considered.

Micromechanics Approach for the Overall Elastic Properties of Ceramic Matrix Composites Incorporating Defect Structures

2021 ◽  
Author(s):  
Rajesh Kumar
Keyword(s):  
Elastic Properties ◽  
Volume Fraction ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Matrix Composites ◽  
Defect Structures ◽  
Modeling Framework ◽  
Linear Elastic ◽  
Elastic Tensor ◽  
The Matrix

Abstract Initial mechanical behavior of Ceramic Matrix Composites (CMCs) is linear until the proportional limit. This initial behavior is characterized by linear elastic properties, which are anisotropic due to the orientation and arrangement of fibers in the matrix. The linear elastic properties are needed during analysis and design of CMC components. CMCs are made with ceramic unidirectional or woven fiber preforms embedded in a ceramic matrix formed via various processing routes. The matrix processing of interest in this work is the Polymer Impregnation and Pyrolysis (PIP) process. As this process involves pyrolysis to convert a pre-ceramic polymer into ceramic, considerable volume shrinkage occurs in the material. This leads to significant defects in the form of porosity of various size, shape, and volume fraction. These defect structures can have a significant impact on the elastic and damage response of the material. In this paper, we develop a new micromechanics modeling framework to study the effects of processing-induced defects on linear elastic response of a PIP-derived CMC. A combination of analytical and computational micromechanics approaches is used to derive the overall elastic tensor of the CMC as a function of the underlying constituents and/or defect structures. It is shown that the volume fraction and aspect ratio of porosity at various length-scales plays an important role in accurate prediction of the elastic tensor. Specifically, it is shown that the through-thickness elastic tensor components cannot be predicted accurately using the micromechanics models unless the effects of defects are considered.

Whisker-Reinforced Ceramic Matrix Composites

MRS Bulletin ◽  
1987 ◽  
Vol 12 (7) ◽  
pp. 66-72 ◽  
Author(s):  
J. Homeny ◽  
W.L. Vaughn
Keyword(s):  
High Temperature ◽  
Energy Dissipation ◽  
Mechanical Performance ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Matrix Composites ◽  
Mechanical Reliability ◽  
Interfacial Bond ◽  
High Fracture ◽  
The Matrix

Whisker-reinforced ceramic matrix composites have recently received a great deal of attention for applications as high temperature structural materials in, for example, advanced heat engines and high temperature energy conversion systems. For applications requiring mechanical reliability, the improvements that can be realized in fracture strength and fracture toughness are of great interest. Of particular importance for optimizing the mechanical reliability of these composites is the effect of the whisker/matrix interfacial characteristics on the strengthening and toughening mechanisms. Whisker reinforcements are primarily utilized to prevent catastrophic brittle failure by providing processes that dissipate energy during crack propagation. The degree of energy dissipation depends on the nature of the whisker/matrix interface, which can be controlled largely by the matrix chemistry, the whisker surface chemistry, and the processing parameters.It is generally believed that a strong interfacial bond results in a composite exhibiting brittle behavior. These composites usually have good fracture strengths but low fracture toughnesses. If the interfacial bond is weak, the composite will not fail in a catastrophic manner due to the activation of various energy dissipation processes. These latter composites tend to have high fracture toughnesses and low fracture strengths. Generally, the interface should be strong enough to transfer the load from the matrix to the whiskers, but weak enough to fail preferentially prior to failure. Thus, local damage occurs without catastrophic failure. It is therefore necessary to control the interfacial chemistry and bonding in order to optimize the overall mechanical performance of the composites.

Multi-Axial Failure of Ceramic Matrix Composite Fiber Tows

2011 ◽  
Vol 78 (3) ◽  
Author(s):  
M. Blacklock ◽  
D. R. Hayhurst
Keyword(s):  
Axial Stress ◽  
Ceramic Matrix Composite ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Composite Fiber ◽  
Woven Composites ◽  
Matrix Composites ◽  
Stress Strain ◽  
Fiber Failure ◽  
Stressed Region

This paper considers the multi-axial stress-strain-failure response of two commercially woven ceramic matrix composites. The different failure mechanisms of uni-axially stressed tows and woven composites are addressed. A model is postulated in which the local transverse and shear stressing, arising from the weave, instantaneously deactivate wake debonding and fiber pullout and initiates dynamic fiber failure; hence, triggering catastrophic failure of the axially stressed region of the tow. The model is shown to predict experimentally measured stress-strain-failure results for the woven composites considered. Simple stress-strain-failure models are also proposed for tows subjected to axial-transverse and axial-shear loadings, but due to the lack of experimental data they have not been validated.

Effect of Microporosity on Damage Initiation in Ceramic Matrix Composites

2019 ◽  
Author(s):  
Suhasini Gururaja ◽  
Abhilash Nagaraja
Keyword(s):  
Gas Turbines ◽  
Ceramic Matrix Composites ◽  
Local Stress ◽  
Ceramic Matrix ◽  
Matrix Composites ◽  
Damage Initiation ◽  
The Matrix ◽  
Homogenization Approach ◽  
Matrix Porosity ◽  
Monolithic Ceramics

Abstract Ceramic matrix composites (CMC) are a subclass of composite materials consisting of reinforced ceramics. They retain the advantages of ceramics such as lower density and better refractory properties but exhibit better damage tolerance compared to monolithic ceramics. This combination of properties make CMCs an ideal candidate for use in high temperature sections of gas turbines. However, modeling the damage mechanisms in CMCs is complex due to the heterogeneous microstructure and the presence of processing induced defects such as matrix porosity. The effect of matrix pore location and orientation on damage initiation in CMCs is of interest in the present work. CMCs fabricated by various fabrication processes exhibit matrix pores at different length scales. Microporosities exist within fiber bundles in CMCs have a significant effect on microscale damage initiation and forms the focus of the current study. In a previous work by the authors, a two step numerical homogenization approach has been developed to model statistical distribution of matrix pores and to obtain the effective mechanical properties of CMCs in the presence of matrix porosity. A variation of that approach has been adopted to model matrix pores and investigate the severity of pores with respect to their location and orientation. CMC microstructure at the microscale has been modeled as a repeating unit cell (RUC) consisting of fiber, interphase and matrix. Ellipsoidal pores are modeled in the matrix with pore distance from the interphase-matrix interface and pore orientation with respect to the loading direction as parameters. Periodic boundary conditions (PBCs) are specified on the RUC by means of constraint equations. The effect of the pore on the local stress fields and its contribution to matrix damage is studied.

scholarly journals Local-Global Analysis of Crack Growth in Continuously Reinforced Ceramic Matrix Composites

1990 ◽  
Vol 112 (4) ◽  
pp. 512-520 ◽  
Author(s):  
R. Ballarini ◽  
S. Ahmed
Keyword(s):  
Global Analysis ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Unidirectional Composite ◽  
Matrix Composites ◽  
Failure Characteristics ◽  
The Matrix ◽  
Parametric Studies ◽  
Heterogeneous Region ◽  
Analysis Models

This paper describes the development of a mathematical model for predicting the strength and micromechanical failure characteristics of continuously reinforced ceramic matrix composites. The local-global analysis models the vicinity of a propagating crack tip as a local heterogeneous region (LHR) consisting of springlike representations of the matrix, fibers, and interfaces. This region is embedded in an anisotropic continuum (representing the bulk composite), which is modeled by conventional finite elements. Parametric studies are conducted to investigate the effects of LHR size, component properties, interface conditions, etc. on the strength and sequence of the failure processes in the unidirectional composite system. The results are compared with those predicted by the models developed by Marshall et al. (1985) and by Budiansky et al. (1986).

scholarly journals Research on the interface properties and strengthening–toughening mechanism of nanocarbon-toughened ceramic matrix composites

2020 ◽  
Vol 9 (1) ◽  
pp. 190-208 ◽  
Author(s):  
Yizhang Liu ◽  
Xiaosong Jiang ◽  
Junli Shi ◽  
Yi Luo ◽  
Yijuan Tang ◽  
...  
Keyword(s):  
Graphene Oxide ◽  
Research Work ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Matrix Composites ◽  
Interface Bonding ◽  
Preparation Methods ◽  
Basic Properties ◽  
The Matrix ◽  
Nanocarbon Materials

AbstractNanocarbon materials (carbon nanotubes, graphene, graphene oxide, reduced graphene oxide, etc.) are considered the ideal toughening phase of ceramic matrix composites because of their unique structures and excellent properties. The strengthening and toughening effect of nanocarbon is attributed to several factors, such as their dispersibility in the matrix, interfacial bonding state with the matrix, and structural alteration. In this paper, the development state of nanocarbon-toughened ceramic matrix composites is reviewed based on the preparation methods and basic properties of nanocarbon-reinforced ceramic matrix composites. The assessment is implemented in terms of the influence of the interface bonding condition on the basic properties of ceramic matrix composites and the methods used to improve the interface bonding. Furthermore, the strengthening and toughening mechanisms of nanocarbon-toughened ceramic matrix composites are considered. Moreover, the key problems and perspectives of research work relating to nanocarbon-toughened ceramic matrix composites are highlighted.

Processing of Non-Oxide Ceramic Matrix Composites: An Overview

2006 ◽  
Vol 50 ◽  
pp. 64-74 ◽  
Author(s):  
Roger R. Naslain
Keyword(s):  
Shear Stress ◽  
Thin Layer ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Oxide Ceramic ◽  
Matrix Composites ◽  
The Matrix ◽  
Low Shear Stress ◽  
Compliant Material ◽  
Low Shear

Ceramic matrix composites (CMCs) comprise a fiber reinforcement embedded in a ceramic matrix, the two main constituents being bonded through an interphase, which is a thin layer of a compliant material with a low shear stress, arresting and deflecting the matrix microcracks formed under load. Non-oxide CMCs, such as C/C ; C/SiC or SiC/SiC, are fabricated from a suitable precursor of the matrix, following a gaseous (CVI-process), a liquid (PIP and RMI processes) or a slurry (SI-HPS) routes. Each of these routes is briefly depicted focusing on fundamental aspects and its advantages and drawbacks discussed. Possible extensions of the processes to new composites are suggested. Finally, a comparison of these techniques, in terms of processability and composites properties is presented.

scholarly journals Local-Global Analysis of Crack Growth in Continuously Reinforced Ceramic Matrix Composites

1989 ◽  
Author(s):  
Roberto Ballarini ◽  
Shamim Ahmed
Keyword(s):  
Global Analysis ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Unidirectional Composite ◽  
Matrix Composites ◽  
Failure Characteristics ◽  
The Matrix ◽  
Parametric Studies ◽  
Heterogeneous Region ◽  
Analysis Models

This paper describes the development of a mathematical model for predicting the strength and micro-mechanical failure characteristics of continuously reinforced ceramic matrix composites. The local-global analysis models the vicinity of a propagating crack tip as a local heterogeneous region (LHR) consisting of spring-like representation of the matrix, fibers and interfaces. This region is embedded in an anisotropic continuum (representing the bulk composite) which is modeled by conventional finite elements. Parametric studies are conducted to investigate the effects of LHR size, component properties, interface conditions, etc. on the strength and sequence of the failure processes in the unidirectional composite system. The results are compared with those predicted by the models developed by Marshall et al. (1985) and by Budiansky et al. (1986).

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